134 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 8. — Mortalities of sea lamprey eggs reared at a 

 constant temperature of 60° F. (10° C.) 



(20 hours) and the next longest between stages 8 

 and 9 (12 hours). Mortality was light the first 

 3 days (2 to 7 percent dead; table 8) and was 

 moderate (14 to 29 percent dead) the next 3 

 days. The death rate increased considerably 

 shortly after the embryos entered stage 9 (gas- 

 trula). Samples on the seventh day contained 56 

 percent of dead eggs. The percentage had 

 reached 99 and 99.5 percent on the 11th and 12tli 

 days, respectively, and all eggs were dead on the 

 13th day. 



Development at 52.5° F. 



Again, an increase of temperature (this time 

 only 2.5° above that of the experiment described 

 in the preceding section) permitted development 



at a faster rate and through a greater number of 

 stages (table 6; fig. 28). Heavy mortality started 

 early, however, the death rate increased as devel- 

 opment progressed (tables 9 and 10; fig. 27), and 

 no embryos survived beyond stage 12 (head stage). 



The early stages (1 to 6) of this experiment pro- 

 ceeded slightly more rapidly than the correspond- 

 ing stages of the 50° F. experiment. The periods 

 of overlap of the earlier stages were nearly equal 

 to those of the 50° F. test, although the length of 

 time for each stage was less at 50° F. than at 52.5° 

 (tables 6, 7, and 9). Stage 9 was prolonged at 

 52.5° F. over a period of approximately 9 days. 

 During this time the number of deaths increased. 

 The relatively few embryos that developed beyond 

 stage 9 progressed through a short stage 10 and a 

 much longer stage 11 (about 4 days). Stage 12 

 was reached by approximately 40 embryos, all of 

 which died. The most frequent symptom of death 

 was disintegration of the anterior region of the 

 embryos. 

 Development at 55° F. 



Development at 55° F. proceeded as far as 

 stage 13 (prehatching). Indeed, the terminal 

 sample included 11 live embryos in this stage 

 (along with some 16,000 dead embryos) but all of 

 them were so defective as to make early death 

 almost certain; they were accordingly classed as 



